In a magneto-optical disk device, the magnetic film is locally heated by projecting a high-powered laser beam onto the magnetic film that is perpendicularly magnetized. By reversing the magnetization direction of the magnetic film to the direction of an external magnetic field through the heat, information is recorded or erased. However, generally speaking, the semiconductor laser tends to be affected by temperatures, and even if the driving current supplied to the semiconductor laser is kept constant, the I-P (driving current--amount of light emission) characteristic varies with temperature changes. For this reason, it is difficult to obtain a stable amount of light emission.
Moreover, when the disc-shaped recording medium is rotated in a constant angular velocity, the closer the position subjected to the irradiation of the laser beam comes to the circumference of the disk, the faster the relative linear velocity between the laser beam and the disc-shaped recording medium becomes. As a result, there arises a problem that irradiation energy applied to the magnetic film differs between the inner portions and the outer portions of the disc-shaped recording medium. Therefore, in the case where the driving current supplied to the semiconductor laser is kept constant regardless of radial positions of the disc-shaped recording medium, it is sometimes difficult to normally carry out recording or erasing of information.
In order to solve this problem, in conventional magneto-optical disk devices, the I-P characteristic is preliminarily tested with respect to the disc-shaped recording medium so that information is recorded and erased by the use of an optimum amount of light emission that is suitable for the associated radial position. In other words, a plurality of radial positions are preliminarily specified on the disc-shaped recording medium, and the tests are made while varying the intensity of the driving current to be supplied to the semiconductor laser so as to determine current values at which optimum amounts of light emission are respectively obtained for the radial positions. Thus, the normal controlling operation of the amount of light during recording and erasing is provided based on the resulting test data.
One of such conventional methods for controlling light amount is disclosed in, for example, Japanese Laid-Open Patent Application No. 33737/1990 (Tokukaihei 2-33737).
Moreover, in conventional methods, the controlling operation is performed for each sector based on timing provided for each sector that is pre-formatted on the magneto-optical disk. For example, Japanese Laid-Open Patent Application No. 66424/1987 (Tokukaishou 62-66424) discloses a method wherein the controlling operation is executed in the above-mentioned manner with respect to the header section whereon no data are recorded, namely, the header section having no fear of damaging data, based on timing provided for each sector that is obtained by reproducing the header section.
Furthermore, various controlling operations utilizing the timing for each sector are executed, for example, through a method disclosed in Japanese Laid-Open Patent Application No. 100902/1991 (Tokukaihei 3-100902).
Pre-formatting is a method for formatting a magneto-optical disk during its manufacturing process by forming a header section for each sector in the form of protrusion and recession. In contrast, besides this method, there is another method wherein a magneto-optical disk is formatted by recording header sections magneto-optically in a magneto-optical disk after the disk has been manufactured. (This method is hereinafter referred to as "soft formatting".)
When this soft formatting is adopted, two types of disks exist: (1) the unused disk before formatted wherein no header sections are provided; and (2) the disk wherein header sections have been provided by means of MO (magneto-optical) signals.
Here, as to light-amount controlling with respect to the disk (1), it is impossible to execute timing control for each sector; therefore, continuous light-amount controlling is required. In contrast, if continuous light-amount controlling is applied to the disk (2), the header sections, which have been formed on the disk, might be damaged. Therefore, as to light-amount controlling with respect to the disk (2), timing controlling for each sector is required.
As described above, in the conventional light-amount controlling methods and the light-amount control devices, it has been impossible to use the same method for controlling light-amount in making tests for recording, reproducing, and erasing with respect to the above-mentioned two types of disks.